Power-assisted steering pump

ABSTRACT

The invention relates to a pump, especially a power-assisted steering pump, comprising a current regulating valve, the current regulating valve comprising a hydraulic resistance, such as a main throttle and a regulating piston, whereby the main throttle can optionally be a regulating pin and an annular orifice.

[0001] The present invention is directed to a pump, in particular to a power-assisted steering pump, having a flow-control valve, the flow-control valve including, inter alia, a hydraulic resistance, such as a primary throttle valve, and a control piston, the primary throttle valve being optionally constituted of a control pin and an annular orifice.

[0002] Pumps of this kind are generally known. Thus, it is typical of power-assisted steering pumps for a flow-control valve to be used, to limit the volumetric flow into the steering system, as of a certain volumetric flow, in response to increasing pump speed caused by increasing engine speed of the combustion engine, and to return the surplus volumetric flow directly via the flow-control valve, internally into the pump again. This means that even at idling speed, for example, the pump is driven by the combustion engine at such a speed that the volumetric flow of, for example, 10 l/min required for the steering system, is available. As driving speed increases and, thus, as the engine speed of the combustion engine increases, the volumetric flow of the pump that continues to rise is apportioned via the flow-control valve to the volumetric flow of approximately 10 l/m, flowing to the steering system, and to an additional limiting volumetric flow, which is returned to the pump's suction side. Flow-control valves are also known, which, in response to increasing engine speed, i.e., increasing motor vehicle speed, reduce the volumetric flow to the steering system, in order to give the driver a more direct steering sensation at high speeds. Flow-control valves of this kind have, for example, a control pin having a conical end, which is positioned in an annular orifice. As the flow-control valve continues to open, the primary throttle valve, made up of this control pin and the annular orifice, closes more and more, thereby reducing the volumetric flow streaming to the steering system. However, in flow-control devices of this kind, no other ways to influence the volumetric flow are possible, and the volumetric flow output to the steering system is influenced virtually only by the pump speed.

[0003] Power-assisted steering pumps having flow-control valves are also known where the primary throttle valve can be adjusted by a solenoid. This means that, in the area of the flow-control valve, the placement of the solenoid is predetermined by the position of the primary throttle valve, so that the possible installation positions of the solenoid valve are limited. Also, more space is required for such a pump, making installation in various engine compartments more difficult.

SUMMARY OF THE INVENTION

[0004] It is, therefore, the object of the present invention to devise a pump which will not have these disadvantages. This objective is achieved by a pump, in particular a power-assisted steering pump, having a flow-control valve, the flow-control valve including, inter alia, a hydraulic resistance, such as a primary throttle valve, and a control piston, the primary throttle valve being optionally constituted of a control pin and an annular orifice, an electrically adjustable bypass throttle valve being configured in parallel to the primary throttle valve. Thus, in accordance with the present invention, the volumetric flow from the pump to the consumer, such as the steering system, is able, in addition, to be electrically influenced. Preferably, the same differential pressure acts on the bypass throttle valve as does on the primary throttle valve.

[0005] One embodiment of the pump in accordance with the present invention is distinguished in that, in response to increasing drive current, the bypass throttle valve reduces the delivery rate from the pump to the consumer. In one other preferred specific embodiment, in response to increasing drive current of the bypass throttle valve, the delivery rate from the pump to the consumer is increased.

[0006] One embodiment is also preferred where the electrically adjustable bypass throttle valve is adaptable to series-produced pumps, so that flexible installation positions of the bypass throttle valve are possible, regardless of where the primary throttle valve provided on the flow-control valve is located in the pump. This has the particular benefit that, depending on the installation situation of an existing pump in a particular engine compartment, the installation location of the additional bypass throttle valve is adaptable to these engine compartment conditions, without adversely affecting the main throttle valve situated in the flow-control valve, and thus the functioning of the flow-control valve.

[0007] One embodiment of the pump in accordance with the present invention is distinguished in that the primary throttle valve of the series-produced pump ensures the basic delivery rate of the volumetric flow for the steering system, above all in the fail-safe case, i.e., when, for example, the electrical power supply fails, and in that the electrically adjustable bypass throttle valve is used for additionally varying the delivery rate to the consumer as a function of various parameters. In this context, in accordance with the present invention, the parameters which are supposed to influence the electrically adjustable bypass throttle valve include parameters such as driving speed, engine speed, cornering behavior, braking characteristics, vehicle stability, steering angle, steering-wheel angular velocity, wheel speeds or wheel slip.

[0008] It is also a distinction of a pump in accordance with the present invention that energy savings may be realized by using the electrical bypass throttle valve in addition to the existing primary throttle valve on series-produced pumps. Moreover, by using the additional electrical bypass throttle valve on series-produced pumps, a pump is able to be produced in accordance with the present invention that may be used for vehicles having active steering systems.

[0009] The present invention is described below in detail, in light of the figures.

[0010]FIG. 1 shows a hydraulic circuit plan of a pump in accordance with the present invention.

[0011]FIG. 2 illustrates the operating range of a pump in accordance with the present invention.

[0012]FIG. 3 depicts one structural design of a pump in accordance with the present invention.

[0013]FIG. 4 shows another structural design.

[0014]FIG. 5 likewise shows another design.

[0015]FIG. 6 is a schematic diagram of a method for determining the solenoid-current driving of the bypass throttle valve.

[0016] A pump system in accordance with the present invention is shown in FIG. 1 in the form of a hydraulic circuit diagram. A pump unit 1 is driven via a drive shaft 3 of a driving mechanism (not shown in greater detail here), such as a belt pulley, by a combustion engine. In response to increasing speed, pump 1 delivers a volumetric flow into interconnection point 5. From interconnection point 5, a connecting line 7 leads to a variable primary throttle valve 9, illustrated by a throttle symbol and an arrow, a further connecting line 11 leads to a control piston of a control valve 13, and a third connecting line 15 leads to an electrically adjustable bypass throttle valve 17. Connecting line 11 leads to an interconnection point 19, from where a connecting line 21 leads to the control piston of control valve 13, while a control line 23 acts on the left side of the control piston. Pressure P1 prevailing at the pump output acts in control line 23 and is likewise active via interconnection point 5 in connecting lines 15, 7, 11 and 21. Via primary throttle valve 9, a volumetric flow may stream by way of connecting line 25 to interconnection point 27, into which a connecting line 29 from electrically adjustable bypass throttle valve 17 also leads. In addition, from a nodal point 27, a connecting line 31 leads to a throttle valve 33 and continues via a connecting line 35 to an interconnection point 37, where a control line 39 acts on the right side of the control piston. In addition, a spring 41 acts on the right side of the control piston of control valve 13. From interconnection point 37, a control line 43 continues to a pressure-limiting pilot valve 45 and via a line 47 to an interconnection point 49 into which outlet line 51 of control valve 13 flows. Via an injector device 53, in which the oil flows streaming from the flow-control valve and pressure-limiting valve may entrain oil from a reservoir line 55, the oil flowing off from flow-control valve 13 and/or from pressure-limiting pilot valve 45 flows again via pump suction line 57 into pump unit 1.

[0017] The following describes the functioning of the pump device: In response to increasing speed of pump unit 1, a volumetric flow is increased via primary throttle valve 9, to consumer 59, such as to a power-assisted steering system. With increasing volumetric flow via primary throttle 9, pressure difference P1 minus P2 increases at the primary throttle valve. Ultimately, pressure difference P1 minus P2, which, together with spring 41, acts on the control piston of control valve 13, becomes so great that pressure P1 is able to displace control piston against pressure P2 and adjust spring 41 to the right, enabling a volumetric flow to flow off over the control piston and be supplied, in turn, to suction side 57 of pump 1. Since, in this representation, control piston 13 is linked via a mechanical connection 61 to variable primary throttle valve 9, in response to an increasing opening movement of piston 13, variable primary throttle valve 9 continues to close, so that with increasing pump speed, a volumetric flow streaming toward the consumer is reduced. Thus, the volumetric flow streaming toward consumer 59 is predetermined by the particular mechanical conditions of control valve 13 and of adjustable primary throttle valve 9, and is not able to be changed further. At this point, to allow additional parameters to act on the level of the volumetric flow to consumer 59, in parallel to primary throttle valve 9, the present invention utilizes electrically adjustable bypass throttle valve 17, which, in response to increasing drive current on a solenoid 63, is able to continuously push up the piston of the bypass throttle valve against a spring force 65, and thus render possible an additional volumetric flow into nodal point 27 and thus to consumer 59. Thus, a volumetric-flow characteristics map is feasible independently of the particular mechanical conditions of the control piston of control valve 13 and of primary throttle valve 9.

[0018]FIG. 2 illustrates the bandwidth of such a volumetric-flow characteristics map. The regulated delivery rate to consumer 59 in l/min, here between 0 and 10 l/min, is plotted over the pump speed in rpm, here from 0 to 6000 revolutions. In this context, a delivery-rate operating-range band 100 is discernible, which, at about 600 rpm, exhibits an average volumetric flow of 4.5 l/min. In response to an increasing speed of up to 6,000 rpm, it falls to an average volumetric flow of 2 l/min. This volumetric-flow band corresponds, for example, to the volumetric flow which is adjusted by the control piston of control valve 13 and variable primary throttle valve 9, the intention being for the bandwidth to include all additional tolerances in the system. By opening electrically adjustable bypass throttle valve 17 from FIG. 1, an additional volumetric flow to the consumer is able to be provided, which, continuing up to maximum opening of bypass throttle valve 17, leads to operating-range band 101 in FIG. 2. Thus, at approximately 1,000 rpm, 8 l/min are realizable, which, at 6,000 rpm, are reduced by variable primary throttle valve 9 to about 6.5 l/min. The continuously variable primary throttle valve 17 makes all characteristic curves between characteristic curves 100 and 101 feasible. Thus, for parking, for example, a high volumetric flow may be provided, which is lowered at a high driving speed, in order to produce a more direct sensation of the steering-wheel forces at the steering wheel. A delivery-rate characteristic curve for the steering system may be adjusted in the same manner in accordance with other vehicle parameters, as well, such as cornering speed, braking characteristics, wheel slip, etc. It is equally possible for the high volumetric flow initially required for parking to be lowered by the variable primary throttle valve relatively quickly to a minimal volumetric flow, thereby adding to energy savings.

[0019] In principle, the approach may be such that variable primary throttle valve 9 ensures the basic pump delivery rate. As in known methods heretofore, various speed-dependent characteristic curves of the basic delivery rate may be realized by the control pin, which is mechanically linked to the control piston of control valve 13. The pump delivery rate may be varied, in addition, by electrically adjustable bypass throttle valve 17, which is connected in parallel to primary throttle valve 9 and is acted upon by same differential pressure P1 minus P2. Depending on the structural design, in response to increasing drive current for solenoid 63, bypass throttle valve 17 may reduce or increase the delivery rate of pump 1 to consumer 59. Therefore, with regard to the fail-safe performance of a pump device of this kind, it is also beneficial that mechanical primary throttle valve 9 continues to function should the electrical power supply fail. This is not so readily feasible when a purely electrically adjustable primary throttle valve is used.

[0020]FIG. 3 depicts the structural adaptation of a variable primary throttle of this kind to a series-produced pump housing. Electrically operable bypass throttle valve 201 is mounted via a fitting 203 on a cover 205 of a series-produced power-assisted steering pump. Cover 205 seals a pump housing 207, in which the flow-control valve, present till now, and the variable primary throttle valve (which are not visible here) are located in a valve housing 209. The volumetric inflow to the consumer is provided by a port 211 at the pump, and the return flow from the consumer and the reservoir by port 213. Depending on the structural conditions in the engine compartment of the pump used till now and shown here, by modifying cover 205 or fitting 203, the position of electrical valve 201 may be varied in a number of ways, without altering the other structural conditions of the pump or even of the vehicle.

[0021]FIG. 4 illustrates how such an electrical bypass throttle valve is adapted to another type of series-produced pump. Here, electrical bypass throttle valve 201 is mounted on pump housing 207 above flow-control valve housing 209, resulting in a vertical attachment in conformance with the installation conditions of this pump. In this pump, the pressure connection to consumer 211 and the suction connection of pump 213 are configured in other positions, so that an available place for positioning the bypass throttle valve may be found in a different way, in conformance with these conditions and the space requirements in the vehicle.

[0022]FIG. 5 shows the same pump type as in FIG. 4, including an axial attachment of electrical bypass throttle valve 201. Depending on the conditions at the installation location of the pump in the engine compartment, the space behind the pump may be used for adapting solenoid valve 201, when no space is available in the areas around valve housing 209, at suction side 213 or at pressure-outlet side 211. In light of these descriptions, one readily discerns that the additional bypass throttle valve, with its flexible installation positions, makes possible a simple adaptation to series-produced pumps.

[0023]FIG. 6 shows a schematic diagram of a method for determining the solenoid-current driving of bypass throttle valve 201. In this context, an electronic computer device determines the solenoid current on the basis of a plurality of input variables, and a solenoid current is output accordingly. Input variables used for the algorithm for determining the solenoid current include driving speed 301, steering-wheel angular velocity 303, engine speed 305 of the combustion engine, and steering angle 307. Steering-wheel angular velocity 303 is generated by a functional unit as a first input variable for a characteristics map 309. Vehicle speed 301 is used as a second input variable for characteristics map 309. Thus, a valve-opening value is mapped in characteristics map 309 as a function of vehicle speed 301 and steering-wheel angular velocity 303. Characteristics map 309 is used, in turn, as first input variable for a second characteristics map 311, which processes engine speed 305 as a second input variable. Thus, in characteristics map 311, a valve-opening value is mapped as a function of characteristics map 309 and of combustion-engine speed 305. Second characteristics map 311 is used, in turn, as first input variable for a functional unit 315, for which a characteristic curve 313 is used as second input variable. Characteristic curve 313 is generated from steering-angle signal 307 and constitutes a valve-opening value as a function of steering angle 307. The output variable of functional unit 315 is the input variable for a functional unit 317 in which the solenoid-current characteristic curve is generated for solenoid current 319 of bypass throttle valve 201 as a function of the valve-opening value. Solenoid current 319 is then made available to the solenoid of bypass throttle valve 201.

[0024] The claims filed with the application are proposed formulations and do not prejudice the attainment of further patent protection. The applicant reserves the right to claim still other combinations of features that, so far, have only been disclosed in the specification and/or the drawings.

[0025] The antecedents used in the dependent claims refer, by the features of the respective dependent claim, to a further embodiment of the subject matter of the main claim; they are not to be understood as renouncing attainment of an independent protection of subject matter for the combinations of features of the dependent claims having the main claim as antecedent reference.

[0026] Since, in view of the related art on the priority date, the subject matters of the dependent claims may form separate and independent inventions, the applicant reserves the right to make them the subject matter of independent claims or of divisional applications. In addition, they may also include independent inventions, whose creation is independent of the subject matters of the preceding dependent claims.

[0027] The exemplary embodiments are not to be understood as limiting the scope of the invention. Rather, within the framework of the present disclosure, numerous revisions and modifications are possible, in particular such variants, elements and combinations and/or materials, which, for example, by combining or altering individual features or elements or method steps described in connection with the general description and specific embodiments, as well as the claims, and contained in the drawings, may be inferred by one skilled in the art with regard to achieving the objective, and lead, through combinable features, to a new subject matter or to new method steps or sequences of method steps, also to the extent that they relate to manufacturing, testing, and operating methods. 

1-11. (canceled). 12: A pump comprising: a flow-control valve having a hydraulic resistance; and an electrically adjustable bypass throttle valve disposed in parallel to the flow control valve. 13: The pump as recited in claim 12, wherein the pump is for a vehicle power-assisted steering system. 14: The pump as recited in claim 12, wherein the flow-control valve includes a control piston and a primary throttle valve. 15: The pump as recited in claim 14, wherein the primary throttle valve includes a control pin and an annular orifice. 16: The pump as recited in claim 12, wherein a volumetric flow rate from the pump to a consumer is electrically changeable. 17: The pump as recited in claim 16, wherein the consumer is a vehicle steering system. 18: The pump as recited in claim 14, wherein a pressure differential acting on the bypass throttle valve is the same as a pressure differential acting on the primary throttle valve. 19: The pump as recited in claim 16, wherein the bypass throttle valve reduces the volumetric flow rate from the pump to the consumer in response to an increasing drive current. 20: The pump as recited in claim 16, wherein the bypass throttle valve increases the volumetric flow rate from the pump to the consumer in response to an increasing drive current. 21: The pump as recited in claim 14, wherein the electrically adjustable bypass throttle valve is installed onto an existing pump having the flow control valve. 22: The pump as recited in claim 14, wherein the primary throttle valve provides a basic volumetric flow rate to a steering system with or without electrical power, and wherein the electrically adjustable bypass throttle valve is configured to modify the basic volumetric flow rate to a modified volumetric flow rate according to at least one parameter. 23: The pump as recited in claim 22, wherein the at least one parameter includes at least one of a driving speed, an engine speed, a cornering behavior, a braking characteristic, a vehicle stability, a steering angle, a steering-wheel angular velocity, a wheel speeds and a wheel slip. 24: The pump as recited in claim 12, wherein the electrical bypass throttle valve saves energy. 25: The pump as recited in claim 12, wherein the electrical active bypass throttle valve enables an active steering system. 